'Mercury poisoning' (also known as 'mercurialism' or 'hydrargyria', or 'acrodynia' when affecting children) is a
disease caused by exposure to
mercury or its
toxic compounds. Mercury is a
cumulative heavy metal poison which occurs in its elemental form,
inorganically as
salts, or
organically as
organomercury compounds; the three groups vary in effects due to differences in their
absorption and
metabolism, among other factors.
[1] However, with sufficient exposure all mercury-based toxins damage the
central nervous system and other
organs or
organ systems such as the
liver or
gastrointestinal tract.
Symptoms typically include sensory impairment (vision, hearing, speech), disturbed sensation and a lack of coordination. The type and degree of symptoms exhibited depend up on the individual toxin, the dose, and the method and duration of exposure.
Due to its
toxicity, there have been campaigns in many countries to ban mercury altogether.
Signs and symptoms
Common symptoms include
peripheral neuropathy (presenting as
paresthesia or
itching, burning or
pain), skin discoloration (pink cheeks, fingertips and toes),
edema (swelling) and
desquamation.
Since mercury blocks the degradation pathway of
catecholamines,
epinephrine excess causes
hyperhidrosis (profuse sweating),
tachycardia,
mercurial ptyalism (
hypersalivation) and
hypertension (high blood pressure). Mercury is thought to inactivate
S-adenosyl-methionine, which is necessary for catecholamine
catabolism by
catechol-o-methyl transferase.
Affected children may show red
cheeks and
nose,
erythematous
lips (red lips), loss of
hair,
teeth, and
nails, transient rashes,
hypotonia and
photophobia. Other symptoms may include
kidney disfunction (e.g.
Fanconi syndrome) or neuropsychiatric symptoms (emotional lability,
memory impairment,
insomnia).
Thus, the clinical presentation may resemble
pheochromocytoma or
Kawasaki disease.
Causes
Mercury poisoning is caused by sufficient exposure to elemental mercury or mercury compounds.
Sources of exposure
Exposure to mercury can occur from breathing contaminated air.
[2]
The majority of mercury pollution in the atmosphere comes from industrial emissions, especially from the burning of
fossil fuels (particularly high-
sulfur coal), mercury mining and smelting, and
chloralkali process plants; improper use or disposal of mercury and mercury-containing objects can also cause mercury exposure, for example, after spills of elemental mercury or improper disposal of
fluorescent light bulbs.
[ Other sources of mercury vapour include crematoriums, waste incinerators, and volcanoes.][ Mercury in the Environment: Implications for Pediatricians, , Lynn R., Goldman, Pediatrics, ]
Mercury exposure can also occur by ingestion of contaminated food and water. The consumption of fish is by far the most significant source of ingestion-related mercury exposure in humans, although plants and livestock also contain mercury due to bioaccumulation of mercury from soil, water and atmosphere, and due to biomagnification by ingesting other mercury-containing organisms.
Mercury and many of its chemical compounds, especially organomercury compounds, can also be readily absorbed through direct contact with bare, or in some cases (such as dimethyl mercury) insufficiently protected, skin. Mercury and mercury compounds are commonly used in chemical laboratories, hospitals, dental clinics, and facilities involved in the production of items such as fluorescent light bulbs, batteries, and explosives.
Toxic effects
Mercury damages the central nervous system, endocrine system, kidneys, and other organs, and adversely affects the mouth, gums, and teeth. Exposure over long periods of time or heavy exposure to mercury vapor can result in brain damage and ultimately death. Mercury and its compounds are particularly toxic to fetuses and infants. Women who have been exposed to mercury in pregnancy have sometimes given birth to children with serious birth defects (see Minamata disease).
Mercury exposure in young children can have severe neurological consequences, preventing nerve sheaths from forming properly. Mercury inhibits the formation of myelin, the building block protein that forms these sheaths.[3]
There is some evidence that mercury poisoning may predispose to Young's syndrome (men with bronchiectasis and low sperm count).[Hendry WF, A'Hern FPA, Cole PJ. Was Young's syndrome caused by mercury exposure in childhood? ''BMJ'' 1993;'307':1579-82. PMID 8292944]
Mercury poisoning in the young has been hypothesized as a cause of autistic behaviors.[4][5] This hypothesis is controversial, as much evidence suggests that about 90% of autism is explained by genetics.[ The genetics of autistic disorders and its clinical relevance: a review of the literature, Freitag CM, , , Mol Psychiatry, 2007 ] The hypothesis has not been confirmed by reliable studies.[6]
Mercury poisoning's effects partially depend on whether it has been caused by exposure to elemental mercury, inorganic mercury compounds (as salts), or organomercury compounds.
Elemental mercury
Pure elemental mercury is moderately absorbed through the skin, rather poorly absorbed through the gastrointestinal tract (often passing through unabsorbed), and readily absorbed as vapor through the lungs. The element is strongly toxic when absorbed as vapor from the respiratory tract, but it is considerably less so when exposure occurs via other routes.
Organic mercury compounds
Compounds of mercury tend to be much more toxic than the element itself, and organic compounds of mercury are often extremely toxic and have been implicated in causing brain and liver damage. The most dangerous mercury compound, dimethyl mercury, is so toxic that even a few microliters spilled on the skin, or even a latex glove, can cause death.[ Dimethylmercury can be fatal within hours or less. One of the chief targets of the toxin is the enzyme pyruvate dehydrogenase (PDH). The enzyme is irreversibly inhibited by several mercury compounds, the lipoic acid component of the multienzyme complex binds mercury compounds tightly (mercury binds to the sulfur atoms in lipoic acid) and thus inhibits PDH.]
Through bioaccumulation in the environment, methyl mercury works its way up the food chain, reaching high concentrations among populations of some species. Larger species of fish, such as tuna or swordfish, are usually of greater concern than smaller species. The U.S. Food and Drug Administration (FDA) advises women of child-bearing age and children to completely avoid swordfish, shark, king mackerel and tilefish and to limit consumption of king crab, snow crab, albacore tuna and tuna steaks to 6 oz. or less per week. However, there is no evidence that moderate consumption of fish in the U.S. poses a significant health hazard. One recent Harvard Medical School study of mothers and their infants suggests that the nutritional benefits of eating fish outweighs the potential drawbacks of methylmercury.[7] In the study, each additional weekly serving of fish consumed by the mother during pregnancy was associated with an increase in infant cognition.
Ethylmercury is a breakdown product of the antibacteriological agent thimerosal which has effects similar but not identical to methyl mercury.
Inorganic mercury compounds
Mercury occurs inorganically as salts such as mercury(II) chloride. Mercury salts primarily affect the gastro-intestinal tract and the kidneys, and can cause severe kidney damage; however, as they can not cross the blood-brain barrier easily, mercury salts inflict little neurological damage without continuous or heavy exposure.[ Toxicity of mercury, , N.J., Langford, Journal of Human Hypertension, ] As two oxidation states of mercury form salts (Hg+1 and Hg+2), mercury salts occur in both mercury(I) (or mercuric) and mercury(II) (mercurous) forms. Mercury(II) salts are usually more toxic than their mercury(I) counterparts because their solubility in water is greater; thus, they are more readily absorbed from the gastrointestinal tract.
Treatment
The Standard of Care for mercury poisoning is chelation therapy using DMSA (in U.S.), DMPS and ALA (in Europe, Russia and former Soviet republics). A study of workers involved in the production of mercurous chloride, showed that the sodium salt of 2,3-dimercapto-1-propanesulfonic acid (DMPS) was effective in lowering the body burden of mercury and in decreasing the urinary mercury concentration to normal levels.[8]
Alternative medicine makes use of these same substances along with others, such as vitamin C (ascorbic acid), EDTA and "high sulfur foods". However, it has been shown that inorganic mercury (Hg2+) bound to EDTA (a necessary step in EDTA-induced mercury chelation) forms a complex (HgEDTA) that is "potentially injurious to the neuronal cytoskeleton".[9]
Some of the toxic effects of mercury are in some cases partially or wholly reversible, either through specific therapy or through natural elimination of the metal after exposure has been discontinued. However, heavy or prolonged exposure can do irreversible damage, particularly in fetuses, infants, and young children.
Prevention
Mercury poisoning can be prevented (or minimized) by eliminating or reducing exposure to mercury and mercury compounds. To that end, many governments and private groups have made efforts to avoid common hazards or to ban mercury altogether.
Regulations
★ There have been growing efforts to limit exposure from all sources. For children, these efforts have centered on reducing mercury exposure in its organic form by limiting consumption of contaminated fish such as tuna and swordfish, and fish caught from mercury-contaminated waters. (AAP advocacy)
★ As a precautionary measure, thimerosal, a mercury-containing preservative is being eliminated from vaccines as quickly as manufacturers can alter their production processes and obtain FDA approval. (AAP advocacy)
★ AAP recommends that pediatricians stop using all mercury-containing devices, including thermometers, and encourage parents to do the same. (AAP advocacy)
Occurrences of mercury poisoning
★ From 1932 to 1968 methyl mercury was released into the sea around the city of Minamata in Kumamoto prefecture, Japan. The toxin bioaccumulated in fish, which when eaten by the local population caused the largest case of mercury poisoning known. Minamata disease caused the deaths of over 1000 people and permanently disabled a great many more.
★ Another case of widespread mercury poisoning occurred in rural Iraq in 1971-1972, when grain treated with a methyl mercury-based fungicide that was intended for planting only was used by the rural population to make bread.
★ In December 1997, a chemistry professor, Karen Wetterhahn, working at Dartmouth College in the United States spilled a drop of dimethyl mercury on her latex glove. She began experiencing the symptoms of mercury poisoning within 5 months of the exposure and, despite treatment, died a few months later.[The Karen Wetterhahn story - University of Bristol web page documenting her death, retrieved December 9th 2006][OSHA update following Karen Wetterhahn's death]
★ In April of 2000, Alan Chmurny attempted to kill a former employee, Marta Bradley, by pouring mercury into the ventilation system of her car.[10]
★ The first emperor of unified China, Qin Shi Huang Di, was driven insane and killed by mercury pills intended to give him eternal life.
Acrodynia epidemic
Acrodynia is a type of mercury poisoning in children characterized by pain and pink discoloration of the hands and feet. The word is derived from the Greek, where ακρος means high (as in:in an extremity) and οδυνη means pain. As such, it might be (erroneously) used to indicate that a patient has pain in the hands or feet. However, acrodynia is a disease rather than a symptom.[Horowitz Y, Greenberg D, Ling G, Lifshitz M. Acrodynia: a case report of two siblings. ''Arch Dis Child'' 2002; '86': 453. PMID 12023189] Also known as pink disease, erythredema, Selter's disease, or Swift-Feer disease, acrodynia was relatively commonplace amongst children in the first half of the 20th century.
Medical procedures
Because elemental mercury often passes through the GI tract without being absorbed, it was used medically for various purposes until the dangers of mercury poisoning became known. For example, elemental mercury was used to mechanically clear intestinal obstructions (due to its great weight and fluidity), and it was a key ingredient in various medicines throughout history, such as blue mass. The toxic effects often were either not noticed at all, or so subtle or generic that they were attributed to other causes and were not recognized as poisoning caused by mercury. While the usage of mercury in medicine has declined, mercury-containing compounds are still used medically in vaccines and dental amalgam, both of which have been the subject of controversy regarding their potential for mercury poisoning.
Thimerosal
Thimerosal, a preservative that contains mercury, has been added in very minute amounts to vaccines to prevent their deterioration since the 1930s.[12] No adverse effects of thimerosal have ever been proven, although some allergic reactions have been noted. However, organizations such as the American Academy of Pediatrics have recommended that the use of thimerosal be reduced as a precautionary measure. Today, with the exception of some flu vaccines, none of the vaccines used in the United States to protect preschool children against twelve infectious diseases contains thimerosal as a preservative.[13]
Dental amalgam
In recent years, some concern has arisen about the potential toxicity of mercury amalgam in dental restorative procedures (''i.e.,'' in tooth fillings).
Mercury poisoning from cosmetics
Some skin whitening products contain the toxic chemical mercury(II) chloride as the active ingredient. When applied, the chemical readily absorbs through the skin into bloodstream.[14][15] The use of mercury in cosmetics is illegal in the United States. However, cosmetics containing mercury are often illegally imported. Following a certified case of mercury poisoning resulting from the use of an imported skin whitening product, the FDA warned against the use of such products.[16][17][18] Symptoms of mercury poisoning have resulted from the use of various mercury-containing cosmetic products.[19][20][21] The use of skin whitening products is especially popular amongst Asian women.[22] In Hong Kong in 2002, two products were discovered to contain between 9,000 to 60,000 times the recommended dose. [23]
Cultural references
★ The phrase "Mad as a hatter" is likely a reference to mercury poisoning, as mercury-based compounds were once used in the manufacture of felt hats in the 18th and 19th century.[1]
★ A 1996 storyline on ''The Bold and the Beautiful'' had Sheila Carter poison Stephanie Forrester with mercury pills.
★ In the anime Fullmetal Alchemist, the child born from Dante and Hohenheim dies of mercury poisoning at the age of 18.
★ In the Adult Swim show Metalocalypse the Queen of Denmark dies after sampling the mercury frosting on William Murderface's birthday cake in the episode "Birthdayface".
★ Mercury poisoning is blamed for animal mutations and illness in Native Americans in the 70's monster movie, ''Prophecy'' (film),(not to be confused with the Christopher Walken film.)
See also
★ Heavy metal poisoning
★ Lead poisoning
★ Minamata disease, industrial mercury pollution
★ Niigata Minamata disease, industrial mercury pollution
References
1. Toxicology and Immunotoxicology of Mercury: A Comparative Review in Fish and Humans, , Leonard I., Sweet, Journal of Toxicology and Environmental Health,
2. ToxFAQs: Mercury
3. http://movies.commons.ucalgary.ca/showcasetv/mercury
4. Autism: a novel form of mercury poisoning, , S., Bernard, Medical Hypotheses,
5. Mercury and autism: accelerating evidence?, Mutter J, Naumann J, Schneider R, Walach H, Haley B, , , Neuro Endocrinol Lett,
6. Incidence of autism spectrum disorders: changes over time and their meaning, Rutter M, , , Acta Paediatr,
7. Maternal Fish Consumption, Hair Mercury, and Infant Cognition in a U.S. Cohort, Emily Oken, Robert O. Wright, Ken P. Kleinman, David Bellinger, Chitra J. Amarasiriwardena, Howard Hu, Janet W. Rich-Edwards, and Matthew W. Gillman, , , Environmental Health Perspectives, 2005
8. DMPS (2,3-Dimercaptopropane-1-sulfonate, Dimaval) Decreases the Body Burden of Mercury in Humans Exposed to Mercurous Chloride, D. Gonzalez-Ramirez, M. Zuniga-Charles, A. Narro-Juarez, Y. Molina-Recio, K. M. Hurlbut, R. C. Dart and H. V. Aposhian, , , Journal of Pharmacology and Experimental Therapy, 1998
9. Duhr EF, Pendergrass JC, Slevin JT, & Haley BE. ''HgEDTA complex inhibits GTP interactions with the E-site of brain beta-tubulin.'' Toxicol Appl Pharmacol. 1993 Oct;122(2):273-80. PMID 8212009
10. 'Mad Scientist': On Court TV, Fatal Chemistry
11. The Rise and Fall of Pink Disease, Ann Dally, , , Social History of Medicine, 1997
12. The Toxicology of Mercury — Current Exposures and Clinical Manifestations, , , , The New England Journal of Medicine,
13. NIP: vacsafe/thimerosal default redirect to ISO thimerosal page
14.
15.
16. FDA bans hydroquinone in skin whitening products
17. FDA bans hydroquinone in skin whitening products
18.
19. Mercury exposure in children: a review, , S. Allen, Countera, ,
20. The toxicology of mercury and its chemical compounds, Clarkson TW, Magos L, , , Crit Rev Toxicol, 2006
21.
22. In a survey, 28% of Koreans and 50% of Philippians say that they use skin whitening products.
23.
Further reading
★ Mercury exposure and public health, Clifton JC 2nd, , , Pediatr Clin North Am, 2007
External links
★ ATSDR - Toxicological Profile: Mercury at CDC
★ National Pollutant Inventory - Mercury and compounds Fact Sheet at Department of the Environment and Water Resources
★ Overview at NIH
★ Mercury activity at National Internet Science Educational Resource
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